1. Field of the Invention
This present invention relates to engineering methods for constructing rechargeable oxide-ion battery ROB cells (hereinafter “ROB cells and stacks”) which include oxygen/air plenums. More specifically, the invention details low cost fabrication methods and oxygen and auxiliary gas feed flows for practical low weight compact ROB cells and stacks.
2. Description of Related Art
Electrical energy storage is crucial for the effective proliferation of an electrical economy and for the implementation of many renewable energy technologies. During the past two decades, the demand for the storage of electrical energy has increased significantly in the areas of portable, transportation, load-leveling and central backup applications. The present electrochemical energy storage systems are simply too costly to penetrate major new markets. Higher performance is required, and environmentally acceptable materials are preferred. Transformational changes in electrical energy storage science and technology are in great demand to allow higher and faster energy storage at lower costs and longer lifetimes necessary for major market enlargement. Most of these changes require new materials and/or innovative concepts, with demonstration of larger redox capacities that react more rapidly and reversibly with cations and/or anions.
Batteries are by far the most common form of storing electrical energy, ranging from: standard every day lead—acid cells, nickel-metal hydride (NiMH) batteries taught by Kitayama in U.S. Pat. No. 6,399,247 B1, metal-air cells taught by Isenberg in U.S. Pat. No. 4,054,729, and to the lithium-ion battery taught by Ohata in U.S. Pat. No. 7,396,612 B2. These latter metal-air, nickel-metal hydride and lithium-ion battery cells require liquid electrolyte systems.
Batteries range in size from button cells used in watches, to megawatt load leveling applications. They are, in general, efficient storage devices, with output energy typically exceeding 90% of input energy, except at the highest power densities.
Rechargeable batteries have evolved over the years from lead-acid through nickel-cadmium and nickel-metal hydride (NiMH) to lithium-ion batteries. NiMH batteries were the initial workhorse for electronic devices such as computers and cell phones, but they have almost been completely displaced from that market by lithium-ion batteries because of the latter's higher energy storage capacity. Today, NiMH technology is the principal battery used in hybrid electric vehicles, but it is likely to be displaced by the higher power energy and now lower cost lithium batteries, if the latter's safety and lifetime can be improved. Of the advanced batteries, lithium-ion is the dominant power source for most rechargeable electronic devices.
What is needed is a dramatically new electrical energy storage device that can easily discharge and charge a high capacity of energy quickly and reversibly, as needed. What is also needed is a device that can operate for years without major maintenance. What is also needed is a device that does not need to operate on natural gas, hydrocarbon fuel or its reformed by-products such as H2. One possibility is a rechargeable oxide-ion battery (ROB), as set out, for example, in application Ser. No. 12/695,386, filed on Jan. 28, 2010, now U.S. Patent Publication No. 2011/0033769, and application Ser. No. 13/167,900 filed on Jun. 24, 2011 (entitled “Construction of Planar Rechargeable Oxide-Ion Battery Cells and Stacks Using Stainless Steel Housing Structures.”)
A ROB comprises a metal electrode, an oxide-ion conductive electrolyte, and a cathode. The metal electrode undergoes reduction-oxidation cycles during charge and discharge processes for energy storage. The working principles of a rechargeable oxide-ion battery ROB cell 1 are schematically shown in FIG. 1. In discharge mode, oxide-ion anions migrate from high partial pressure of the oxygen side (air electrode—2) to low partial pressure of the oxygen side (metal electrode—4) under the driving force of the gradient oxygen chemical potential. Electrolyte is shown as 3. There exist two possible reaction mechanisms to oxidize the metal. One of them, solid-state diffusion reaction as designated as Path 1, is that oxide ion can directly electrochemically oxidize metal to form metal oxide. The other, gas-phase transport reaction designated as Path 2, involves generation and consumption of gaseous phase oxygen. The oxide ion can be initially converted to a gaseous oxygen molecule on a metal electrode, and then further reacts with metal via solid-gas phase mechanism to form metal oxide. In charge mode, the oxygen species, released by reducing metal oxide to metal via electrochemical Path 1 or solid-gas mechanism Path 2, are transported from a metal electrode back to an air electrode.
During discharge/charge cycles metal redox reactions induce significant volume variation, for instance, if iron (Fe) metal is used, the volume change associated with the reaction of Fe+½O2=FeO is 1.78 times. Therefore, the metal electrode must be appropriately designed so that the drastic volume variation can be properly accommodated. For energy storage application, oxide ion must be transported across the electrolyte between a metal electrode and a cathode to carry electrical charge. Therefore, the metal electrode must be hermetically sealed to prevent direct contact with an oxygen-containing environment (for example, air). Otherwise, oxygen in air will directly consume the metal without involving charge transfer between electrodes, which will lead to self discharge.
The cell voltage for each individual ROB cell is limited in most cases, for practical applications where certain voltage output is demanded, ROB cells must be connected together to form a stack to raise the voltage of a ROB device. Means must be also found to provide oxygen and steam or hydrogen to the stack cells via gas plenums. Additionally, weight must be lowered to make the ROB stacks practical. Thus, there is a need of engineering methods to construct an ROB stack using single ROB cells containing various gas plenums.
It is a main object of this invention to provide ROB cell and stack designs that supply the above needs by using cost-effective materials and processing techniques.